1. Field of the Invention
In the printing industry, the processes in current use include lithography (52% share of the industry), gravure (18%), flexography (19%), letterpress (5%), and screen printing and other miscellaneous processes (6%).
Printing inks that are conventionally used in these applications are multicomponent systems comprising: (1) the pigment; (2) a hydrocarbon and/or alkyd resin; (3) a hydrocarbon solvent; and (4) optional additives. For example, a typical petroleum-based, black, litho-news ink would be comprised of 15-20% carbon black as the pigment, 15-25% hydrocarbon or alkyd resin, and 50-70% mineral oil solvent. Nearly 500 million kilograms of inks for these applications are produced domestically each year. This volume of production represents a substantial consumption of a petroleum-based fraction. The petroleum oil shortage in the mid 1970's stimulated research to find alternatives to mineral oil and other petroleum products in ink formulations.
This invention relates to vegetable oil-based inks which do not require petroleum products and which possess the desirable properties for most printing ink applications.
2. Description of the Prior Art
Inks containing vegetable oils have been formulated for various specialized applications. For example, Ono et al. [Japanese Kokai Tokkyo Koho JP 61/123,681] show hot-melt copying inks comprising a pigment in a nondrying vegetable oil and vegetable wax base. Kuzuwata [Japanese Kokai Tokkyo Koho JP 63/277,287] teach stencil printing inks comprising a minor proportion of vegetable oil in a predominantly water-based formulation. Gupta et al. [Indian Patent IN 154,760] report an ink for stamp cancellation containing inedible vegetable oils, dispersing agents, and pigments.
Vegetable oils polymerized by oxygenation were evaluated for use as vehicles for typewriter and printer ribbon inks by Richlin et al. [Amer. Ink Maker 65(5): 14-18, 48 (May 1987)]. Also, a vehicle comprising a blend of ester gum, alkyd, cetanol, and vegetable oil for use in discharge printing of fabrics has been taught by Kobayashi [Japanese Patent 78/17,716].
In the early 1980's, the American Newspaper Publishers Association (ANPA) directed a research effort on developing a nonpetroleum-based vehicle for newsinks. A series of ink formulations were patented by Moynihan comprising a blend of "gilsonite" (uintaite) and tall oil fatty acids together with carbon black pigment. U.S. Pat. No. 4,419,132 relates to a printing ink comprising 16.5-21.5% carbon black, 16.4-25.1% "gilsonite", and 54.9-64.4% tall oil fatty acid. U.S. Pat. No. 4,554,019 is drawn to a letterpress ink having 6.0-19.8% carbon black, 16.4-26.3% "gilsonite", and 52.7-70.5% tall oil fatty acid. The offset printing ink of U.S. Pat. No. 4,519,841 comprises 10-27.8% carbon black, 17.6-23.5% "gilsonite", and 50.1-54.9% tall oil fatty acid. Acceptance of these inks by the industry has been limited by the cost and availability of tall oil and the difficulty of equipment cleanup caused by the "gilsonite". A later approach by ANPA to produce a vegetable oil-based ink vehicle resulted in a lithographic newsink comprising 50-60% alkali-refined soybean oil, 20-25% of a hydrocarbon resin ("Picco 5140"), and about 20% carbon black pigment. Widespread commercial acceptance of this ink has been inhibited by the cost, which is 50-70% more than traditional petroleum-based black inks.
Despite advances in the art made by the ANPA and others, the industry has continued to seek a nonpetroleum-based printing ink vehicle which would: (1) be cost competitive with petroleum-based inks; (2) not require any petroleum-derived component; (3) resist ruboff on hands and clothing; and (4) enable formulation over a wide range of viscosities required by various printing applications.